Rotary pumps for abrasive fluids, commonly used as chemical pumps, concrete pumps, or gravel pumps, have as a rule, cylinders made from a hard material in which a piston reciprocates. The bottom of these pistons consists of a rubber or rubber-like material. These pumps suffer extremely high wear and frequent freezing, by formation of a deposit between the piston and the cylinder.
The invention relates to reciprocating pumps, where pistons and cylinders, as well as the inlet and outlet valves, consist of a material with a hardness above the hardness of the abrasives to be conveyed. The invention reduces wear by providing relative rotational velocity between piston and cylinder. This rotation enables the piston to glide without making contact with the cylinder. Thus piston and cylinder execute a turning movement with a high enough speed so that a hydro-dynamic film develops in the working clearance. This movement around the axis of the piston is superposed on axial movement between piston and cylinder. According to the invention, the piston, as well as the cylinder, consist of materials with a hardness higher that that of the abrasive particles if it is intended to convey such liquids. To avoid dirt accumulation, the cylinder can be formed with one annular area where dirt particles can settle. As soon as the dirt particles build up on the surface of the piston, they are brought by the piston ring into said annular space being stripped away when the piston reverses. The principle of the invention is suitable for all liquids from low to high viscosity, but also for gases, so that the invention is also appropriate for conveyance of gas and also of gas loaded with abrasive powder.